1. Field of the Invention
The present invention relates to a method and apparatus for generating an image, and more particularly, to a method and apparatus for generating an image which can generate a colorimetrically-corrected high-dynamic range (HDR) image by acquiring a plurality of images through multiple exposures, white-balances the plurality of images with respect to a reference correlated color temperature (CCT), and synthesizing the white-balanced images.
2. Description of the Related Art
In recent years, the distribution of digital cameras and devices equipped with high-resolution cameras such as camera phones has been widespread. These cameras generally include lenses and image sensors.
Lenses collect light reflected from a subject, and image sensors detect light collected by lenses and convert it into electrical image signals. Image sensors consist generally of solid-state image sensors. Examples of the solid-state image sensors include a charge coupled device (CCD) and a complementary metal oxide semiconductor (CMOS).
Image sensors of cameras may include a color filter array (CFA) which consists of a mosaic of color filters in which each color filter filters light reaching each pixel. Since image sensors are highly sensitive to near-Infrared (NIR) light radiation, image sensors of cameras may also include a NIR shield filter which is mounted on a CFA for preventing image discolorations caused by NIR light radiation.
In the meantime, in the case of capturing images in a high-illumination or low-illumination environment or in a sharp contrast environment with backlighting, conventional image sensors may not be able to accurately render color images because their inherent limitations in dynamic range. As a result, the rendered image will loose information either in the shadows or in the highlights for HDR scenes.
In order to address this problem, high dynamic range (HDR) image sensors capable of accurately capturing images even in a high-illumination or low-illumination environment or in a sharp contrast environment with backlighting have been developed. However, HDR image sensors are generally expensive sensors mainly used for security and military purposes and they are not suitable for consumer products due to their cost and complexity.
Conventionally, an HDR image is created by generating a plurality of images using different light exposure amounts and synthesizing the images.
For example, in the case of capturing images of a subject in a backlighting state while varying an exposure amount, short-exposure images contains highlighted area without saturation but dark shadow areas will not be visible, whereas long-exposure images may have visibility in the dark areas but lost information in bright areas due to saturation. However, HDR images can be obtained by combining a short-exposure image with a long-exposure image.
Conventional methods of generating an HDR image involve encoding a number of images into red-green-blue (RGB) images through radiometrical correction and synthesizing the RGB images and generally result in images with poor color fidelity. A plurality of images obtained using different exposure durations generally have different white points. For example, long-exposure images have high correlated color temperatures (CCTs) in shadow areas, whereas short-exposure images have lower CCTs from high-illuminated areas. However, in conventional methods of generating an HDR image, a plurality of images are white-balanced without consideration of the white points of the images, and then the white-balanced images are synthesized, thereby resulting in an HDR image with poor color fidelity.